Apparatus of processing a sample surface and method thereof

ABSTRACT

A surface processing apparatus is provided. In the apparatus, an etching rate ratio of an organic material such as a BARC of anti-reflective film to a resist of mask forming a pattern, that is, a selective ratio is high, the anti-reflective film being a means for forming the pattern with a high accuracy in surface processing of a semiconductor.  
     In the surface processing apparatus using a plasma, a deposition gas is added to a light element of hydrogen as the etching gas. Ions accelerated by a bias electric power supply accelerate etching reaction. Sputtering at edges of the mask can be reduced by using the light element of hydrogen as the etching gas, and the selective ratio of the anti-reflective film to the masking material can be increased by mixing the deposition gas with the hydrogen.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a surface processing apparatusand a surface processing method for a sample such as a semiconductorelement and, more particularly to a surface processing apparatus and asurface processing method suitable for performing etching and filmforming on a semiconductor surface using a plasma.

[0002] Apparatuses widely used for processing such as etching and filmforming of a semiconductor element are apparatuses using a plasma. Thepresent invention can be applied to such apparatuses using a plasma, buthere, a conventional technology will be explained in taking an apparatuscalled as an ECR (electron cyclotron resonance) type among them as anexample. In the apparatus of this type, the plasma is generated by amicrowave in a vacuum chamber applied with a magnetic field from theexternal. A bias voltage is applied to a sample in order to accelerateions incident to the sample. The apparatus is used for film depositionas well as etching.

[0003] Recent semiconductor elements are required to be processed withhigh accuracy as the structure of semiconductor elements becomes finer.Therefore, a new technology is also required to improve the dimensionalaccuracy of a masking pattern in order to process the etched materialhighly accurately. As a method of controlling dimensions in forming apattern of the masking material, a technology using an anti-reflectivefilm such as BARC (bottom anti-reflective coating) is used in order toprevent reflection of light such as ultraviolet light and to exposefinely and accurately. In general, the anti-reflective film is a filmmade of a material which is the same organic group as a material usedfor the resist, and the anti-reflective film is etched by a fluorocarbongroup gas or a halogen group gas mixed with oxygen, and the selectiveratio of the anti-reflective film material to the masking material atprocessing the anti-reflective film is nearly 1. Further, edge portionsof the masking pattern are apt to be cut down by sputtering at theetching, which is a trouble at processing the base etched material.(Refer to FIG. 3 (b))

SUMMARY OF THE INVENTION

[0004] In order to solve the above-mentioned new problem, an object ofthe present invention is to provide a surface processing apparatus and asurface processing method in which the selective ratio, that is, a ratioof etching rate of the organic group film such as the BARC to the filmmade of the same group material such as the resist is increased, and thesurface processing is performed while an initial shape of the resist ischanged as small as possible.

[0005] The present invention is characterized by an apparatus ofprocessing a sample surface comprising a vacuum chamber; a means forgenerating a plasma in the vacuum chamber; a sample table for mounting asample to be performed with surface processing using the plasma; and anelectric power supply for applying a radio frequency bias to the sample,the surface processing of the sample being performed using a maskingmaterial and an anti-reflective film, which further comprises a meansfor introducing a mixed gas of hydrogen gas and a deposition gas as anetching gas into the vacuum chamber.

[0006] Further, the present invention is characterized by a method ofprocessing a sample surface which performs surface processing of asample by using a plasma by generating the plasma in a vacuum chamber;applying a radio frequency bias to a sample table mounting the sample;using a masking material and an anti-reflective film, the methodcomprising the step of introducing a mixed gas of hydrogen gas and adeposition gas as an etching gas into said vacuum chamber.

[0007] Further, the present invention is characterized by that an amountof the deposition gas added to the hydrogen gas is set to an amount E0at which a cut-down amount of the masking material becomes zero.

[0008] According to the present invention, the anti-reflective film canbe highly accurately etched by using a light element of hydrogen as theetching gas to reduce the cut-down amount of edges of the maskingmaterial of resist caused by sputtering and at the same time by mixingthe deposition gas with the hydrogen gas to increase the selective ratioof the anti-reflective film to the masking material of resist.

BRIEF DESCRIPTION OF DRAWINGS

[0009]FIG. 1 is a diagram showing the overall construction of an etchingapparatus to which the present invention is applied.

[0010]FIG. 2 is a graph showing the relationship between the etchingrates of a BARC and a resist depending on the added amount of adeposition gas.

[0011]FIG. 3 is a view showing differences in etched shapes depending onpresence or absence of an etching gas and a deposition gas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Embodiments of the present invention will be described below.

[0013]FIG. 1 is a schematic diagram showing a plasma etching apparatusto which the present invention is applied. The apparatus is a plasmaetching apparatus utilizing electron cyclotron resonance. A coil 2 forgenerating a magnetic field for the electron cyclotron resonance (ECR)is arranged around an etching chamber 1 of vacuum chamber. An etchinggas is supplied through a gas supply pipe 4 which is connected to a gassource through a mass flow controller 3, and introduced into the etchingchamber 1 from a gas supply plate 5 made of silicone or glass formcarbon having several hundreds fine holes having a diameter of 0.4 to0.5 mm.

[0014] A disk-shaped antenna 6 for radiating a microwave of the UHF bandis arranged above the gas supply plate 5, and the microwave to theantenna 6 is transmitted from an electric power supply 7 through amatching circuit 8 and a guide tube 9. The microwave is radiated fromthe periphery of the antenna 6, and a resonance electric field in aspace above the antenna 6 is introduced into the etching chamber througha dielectric body 10. The frequency of the microwave is selected a valuefrom a band which can heat the plasma up to a low electron temperatureof 0.25 eV to 1 eV, that is, it is within a range of 300 MHz to 1 GHz.In the present embodiment, a frequency band near 450 MHz was used.Quartz or alumina may be used for the dielectric body 10. Otherwise, aheat-resistant polymer having a small dielectric loss such as polyimidemay be used.

[0015] A wafer mounting electrode 11 is arranged below the gas supplyplate 5, and a wafer 12 is supported on the wafer mounting electrode byelectrostatic attraction (an electric power supply for the electrostaticattraction is not shown). In order to draw the ions in the plasma intothe wafer 12, a radio frequency bias is applied to the wafer mountingelectrode 11 from a radio frequency electric power supply 13.

[0016] Temperature of the antenna 6 and an inner wall 14 of the etchingchamber are controlled. That is, the temperature is controlled byintroducing a coolant into the antenna 6 and the inner wall 14 of theetching chamber from a temperature controller, not shown, to maintainthe antenna 6 and the inner wall 14 at a constant temperature. In thepresent embodiment, the temperature is controlled so that the antenna 6and the inner wall 14 was maintained at a temperature of 30 to 80° C.

[0017] A turbo molecular pump having an evacuating speed of 2000 to 3000L/s is arranged in a vacuum chamber directly connected to the etchingchamber 1. A conductance valve, not shown, for controlling theevacuation speed is arranged at an opening portion of the turbomolecular pump to adjust the evacuation speed in order to attain a flowrate and a pressure suitable for the etching. Further, a stop valve isprovided in order to isolate the turbo molecular pump at opening theetching chamber to atmosphere.

[0018] An embodiment of BARC etching using the plasma etching apparatusin accordance with the present invention will be described below.

[0019] A wafer is loaded from a transfer chamber into the etchingchamber 1 under a condition evacuated to a high vacuum using a transferarm, not shown, and transferred onto the wafer mounting electrode 11.After the transfer arm is drawn back and a valve between the etchingchamber 1 and the transfer chamber is closed, the wafer mountingelectrode 11 is moved upward and stopped at a position suitable foretching. In the case of the present embodiment, the distance between thewafer 12 and the gas introducing plate 5 (distance between theelectrodes) was set to 50 mm to 100 mm.

[0020] A mixed gas of H₂ and N₂ was used as the etching gas, and H₂ andN₂ were introduce at the flow rates of 100 sccm and 5 sccm,respectively. CHF₃ was added to the mixed gas as a deposition gas. Theoutput power of the UHF microwave electric power supply was set to 1.5kW, and the output power of the bias electric power supply 12 to thewafer was set 60 W. A resonance magnetic field of 0.016 T of UHFmicrowave 450 MHz was generated between the gas supply plate 5 and thewafer mounting electrode 11 (that is, the wafer 12). Then, the microwaveelectric power supply 7 was operated. Thereby, a strong plasma wasgenerated in the ECR region of the magnetic field intensity of 0.016 Tby the electron cyclotron resonance.

[0021] It is necessary that the incident ion density on the surface ofthe wafer 12 is made uniform in order to make the etching propertyuniform. An optimal ion density distribution can be obtained because theECR position can be freely adjusted using the magnetic field coil 2. Inthe present embodiment, the shape of the ECR region was formed in aconvex state to the wafer 12 side.

[0022] After the plasma is ignited, a high voltage is applied to thewafer electrode 11 from a direct current electric power supply, notshown, connected to the radio frequency electric power supply 13 inparallel to electrostatically attract the wafer 12 onto the wafermounting electrode 11. Helium gas is introduced to the backside surfaceof the elecrostatically attracted wafer 12, and temperature control ofthe wafer is performed between the wafer mounting surface of the wafermounting electrode 11 temperature-controlled by a coolant and the waferthrough the helium gas.

[0023] Next, the radio frequency electric power supply 13 is operated toapply the radio frequency bias to the wafer mounting electrode 11. Bydoing so, ions are vertically incident to the wafer 12 from the plasma.When the bias voltage is applied to the wafer 12, etching is initiated.The etching is terminated in a preset etching time. Otherwise, thechange in a light emission intensity of the plasma caused by a reactionproduct is monitored, and an etching termination time is obtained byjudging the etching termination, and then the etching is terminatedafter performing appropriate over-etching. The termination of etching isthe time when the application of the radio frequency bias voltage isstopped. At the same time, the supply of the etching gas is alsostopped.

[0024] Next, a process to detach the electrostatically attached wafer 12from the wafer mounting electrode 10 is necessary, and in this processargon or a kind of gas actually used in the etching is used as adischarging gas. After stopping the supply of the electrostaticattracting voltage and the power supply line is grounded, thedischarging is performed for approximately 10 seconds while themicrowave is being discharged. By doing so, the charge on the wafer 12is removed to the ground through the plasma, and consequently the wafer12 can be easily detached. After completion of the discharging process,the supply of the discharging gas is stopped and the supply of themicrowave is also stopped. Further, the current supply to the coil 2 isalso stopped. The level of the wafer mounting electrode 11 is lowereddown to the wafer transfer position.

[0025] After that, the etching chamber 1 is evacuated to a high vacuumfor a while. At the time when the high vacuum evacuation is completed,the valve between the transfer chamber and the etching chamber is openedand the transfer arm is inserted to receive and unload the wafer 12.When there is a next wafer to be etched, the new wafer is loaded and theetching is performed according to the above-mentioned procedure.

[0026] The above is a typical flow of the etching process.

[0027] An effect of adding a deposition gas will be briefly describedbelow. FIG. 2 is a graph showing the relationship between the addedamount of CHF₃ of one of deposition gases and the etching rates of aBARC and a resist depending on, and FIG. 3 is a view showing etchedshapes.

[0028] It can be understood from FIG. 2 that as the amount of theadditive gas is increased, the etching rate of the resist 15 is largelydecreased, that is, cut down not so much though the etching rate of theBARC 16 is decreased not so much. However, when the amount of theadditive gas exceeds a a value, the resist 15 is accumulated to thecontrary. Therefore, at an added amount E0 of the gas in which thecut-down amount of the resist becomes zero, etching having the selectiveratio of infinity can be performed. It is practical that the amount ofadditive gas is set to a value around the amount E0 and within a rangein which a selective ratio of the anti-reflective film to the maskingmaterial is larger than 2.

[0029]FIG. 3 (a) a view showing an initial shape of a sample to beetched. FIG. 3 (b) a comparative view showing an etched shape which isetched through a conventional technology, that is, using a mixed gas ofhalogen and O₂ as the additive gas. In the conventional technology, edgecutting-down appears at an opening portion of the resist.

[0030] On the other hand, in an embodiment of the present invention,that is, in a case where hydrogen is used as the main etching gas and noadditive gas is not mixed, an etched shape becomes as shown in FIG. 3(c). Edge cutting-down at an opening portion is reduced compared to thatin the conventional technology because a light element of hydrogen isused as the main etching gas. Further, by mixing an additive gas tohydrogen (H₂+CHF₃), etching with edge cutting-down of the resist can beperformed.

[0031] In regard to the adding amount of CHF₃ in the present embodiment,the flow rate of CHF₃ was varied from 0 sccm to 2 sccm and 8 sccmagainst the flow rates of H₂ of 100 sccm and N₂ of 5 sccm. The cut-downamounts of the resist of masking material after etching the BARC havinga film thickness of 80 nm under the above conditions were 120 nm to theinitial film thickness of 720 nm when the added amount of CHF₃ was zero,and 0 nm when the added amount of CHF₃ was 2 sccm. On the contrary, whenthe added amount of CHF₃ was 8 sccm, the sedimentation was 83 nm.Therefore, by etching the BARC under the condition of the added amountof CHF₃ E0=2 sccm, etching of the selective ratio to the maskingmaterial of infinity can be performed. Further, because the lightelement of hydrogen is used as the main gas of the etching gas, thecut-down amount of edges of the opening portion of the resist caused bysputtering is very small.

[0032] The reason why the resist is not cut down but only the etchingreaction of the BARC made of the same kind material is progressed isconsidered that by introducing CHF₃ as the deposition gas, a CH groupsediment having a strong deposition property is accumulated only on theresist surface so much as to inhibit the etching reaction. Although thepresent embodiment has been described on the premise that CHF₃ is usedas the deposition gas, the deposition gas is not limited to CHF₃, andany gas capable of producing a CH group sediment which reacts withhydrogen and has a high adhesive coefficient may be used.

[0033] Although the present embodiment has been described on the premisethat the UHF type ECR plasma etching apparatus is used, the apparatus isnot limited to the UHF type ECR plasma etching apparatus, and the otherplasma source may be used. Therefore, the present invention can beapplied to an induction type plasma apparatus other than the microwavetype.

[0034] Further, although the temperature control in the embodiment isperformed using a coolant, it is not limited to the coolant, and watercooling, forced cooling by gas, or use of a heater, lamp heating usinginfrared rays may be used.

[0035] As described above, in the present invention, the selective ratioof the BARC (the anti-reflective film) to the resist of mask made of thesame group material can be increased, and at the same time the BARC canbe etched with maintaining the initial shape of the resist by the effectof using the etching gas mainly composed of the light element ofhydrogen and adding the deposition gas.

[0036] As having been described above, according to the presentinvention, an organic material such as the material of BARC can beetched with a high selective ratio to the same find of materials usedfor the resist or the like and with maintaining the initial shape of theresist. That is, the sputtering property in the edge portions of themask is reduced by using the light element of hydrogen as the etchinggas, and the selective ratio of the BARC material to the maskingmaterial can be increased by mixing the deposition gas with the etchinggas. By the synergistic effect, an anti-reflective film can be etchedwith a high selective ratio while an initial shape of the resist ischanged as small as possible.

What is claimed is:
 1. An apparatus of processing a sample surfacecomprising a vacuum chamber; a means for generating a plasma in saidvacuum chamber; a sample table for mounting a sample to be performedwith surface processing using said plasma; and an electric power supplyfor applying a radio frequency bias to the sample, the surfaceprocessing of the sample being performed using a masking material and ananti-reflective film, the apparatus further comprising means forintroducing a mixed gas of hydrogen gas and a deposition gas as anetching gas into said vacuum chamber.
 2. An apparatus of processing asample surface according to claim 1 , wherein an amount of saiddeposition gas added to said hydrogen gas is set to a value, said valuebeing around an amount E0 at which a cut-down amount of said maskingmaterial becomes zero and within a range in which a selective ratio ofsaid anti-reflective film to said masking material is larger than
 2. 3.A method of processing a sample surface which performs surfaceprocessing of a sample by using a plasma by generating the plasma in avacuum chamber; applying a radio frequency bias to a sample tablemounting the sample; using a masking material and an anti-reflectivefilm, the method comprising the step of introducing a mixed gas ofhydrogen gas and a deposition gas as an etching gas into said vacuumchamber.
 4. A method of processing a sample surface according to claim 3, wherein an amount of said deposition gas added to said hydrogen gas isset to a value, said value being an amount E0 at which a cut-down amountof said masking material becomes zero.
 5. A method of processing asample surface according to any one of claim 3 and claim 4 , whereinsaid deposition gas mixed with said hydrogen gas is a gas containingcarbon as a constituent element.
 6. A method of processing a samplesurface according to any one of claim 3 and claim 4 , wherein saiddeposition gas contains one kind selected from the group consisting ofCHF₃, CH₂F₂ and CF₄.